Aerobatic Loops

[Tim Cheal]

continued....

Now imagine this in our outside loop (a manoeuvre I have always known as a ’bunt’ but other readers have different definitions for this). If we start at the top and push (as required in the B test, and hence I believe this is the more more routine way of starting the outside loop) then gravity initially helps our aircraft nose to drop, but as our nose drops we need to increase the G to counter the affect of gravity now starting to work against our direction of turn we need extra MINUS G to keep the aircraft ‘bunting’ (we are using the same principle as the loop, and the highest G will be needed at the bottom of the manoeuvre when the aircraft is inverted). We may also be experiencing an increase in airspeed, and to maintain the ‘bunt’ we would need to increase elevator input even more (push more). There comes a point where structurally we simply can’t continue, and I suspect this is where our wings have decided to part company in the past (and in one model many years ago it caused quite a hole in the ground!). Hence, whilst I agree with the points already raised for the most part, there is definitely a difference between an inside and an outside loop, especially when the outside loop is started from the top.

However, if we invert and push our way around the manoeuvre (as suggested by some others) we need the maximum G at the bottom of the bunt to push upwards, which is at the start of the manoeuvre the G reduces and gravity helps us over the top of the bunt, and when we return to inverted we should need no more push than already used to start the manoeuvre. Altogether a much less stressful manoeuvre in every sense!

So, my thoughts are, you need to start the inside loop by using less elevator input, or from a faster speed and pull less, or probably a combination of the 2. For outside loops try starting from inverted and pushing upwards initially. This will give you much more confidence in the ability to control the most hairy part, where the aircraft is accelerating towards the ground and approaching the inverted.

Sorry if that is repetitive in places!

[Bob Cotsford]

Excellent explanation of how to execute true aerobatic loops and bunts Tim. The last thing you want is to pull more up elevator as you go over the top of a loop, just the opposite, and the need for more up on the last quarter is why some models can flick out at this point, similarly with bunts the third quarter is where things go wrong because of the extra down needed.

However, for true geometric figures you also need to adjust the elevator to compensate for wind drift which on a windy day can need the opposite of the method for calm weather - whoever said a loop was simple?

[Peter Jenkins]

Tim - all good stuff, but, with respect, you have omitted mention of the throttle. As we all know, model aeroplanes are grossly overpowered compared with full size aircraft. Aerobatic model aeroplanes are even more so. A good aerobatic model will accelerate upwards with full power when vertical. That leads to the ability to fly at constant speed around a manoeuvre - one of the aims in today's precision aerobatics, hence oodles of power. That also means that the throttle is not an on off switch but one that is being constantly adjusted to match the position of the aircraft. At the risk of overpowering the OP, I did write a section on aerobatic manoeuvres including loops. You can find the looping description here at the post dated 6/12/2013 17:19:01. Be warned it is a long series of posts that covers trimming and flying a great many manoeuvres as well as how to fly the B.

You are right about the highest G being at the bottom of the loop or bunt. G is your enemy on bottom half of the loop but increasingly your friend as you go over the top. I've not seen any aerobatic aircraft clap hands at the bottom of a loop/bunt so I assume this might have been due to some pre-existing damage or an inappropriate airframe. Most model aeroplanes are heavily over engineered compared with full size.

[Ross McWhirter]

Thanks both very much for the comprehensive Advice. I'll practice paying attention to your comments.

[Tim Cheal]

Thanks Bob and Peter, all agreed - I just wish I could do it!

I followed your thread on the aerobatics thank you Peter, and throughly enjoyed it, I should have re-read it before posting my comments above.

To be fair my model dived vertically into the ground, I was very young and couldn't afford much in terms of equipment, so I was never sure if the wings had come adrift or one of my "Gem" servos had jammed.

Tim